OP, my two cents:
Litter boxes: I have a sensitive cat (male). We have had three cats (only two now, sadly). I realized I was wasting time with regular litter boxes. I went out and bought the biggest rubbermade containers I could find. High sides are a plus. I cut a hole in the side for the “sensitive cat” to not have an excuse to not use it. I dressed them up by putting them in IKEA chests (the ones with the slatted sides, so lots of ventilation). I bedded each one really deep. Worked like a charm.
Health issue: The Sensitive One started peeing randomly again about 10 months ago. I couldn’t come up with a why, but decided I really should get him checked out medically. Turns out he had developed stones the size of small peas. He had to have major surgery to remove them, but he was peeing EVERYWHERE and out of the blue prior to this discovery. Like, I would find new pee three times a day. It was awful and I threw away A LOT of pillows (he prefers pillows. Cats are so weird with their individual quirks). So, you seriously might want to try to catch who is peeing and whisk them off to the vet. If it hurts when they pee where they are supposed to, they will try to find a place that doesn’t hurt. Probably your pillow. And you will probably discover it late at night when you lay your exhausted head onto a crusty layer of dried cat piss.
Good luck!